1. Field of Disclosure
The present invention relates to a method for predicting machining quality of a machine tool. More particularly, the present invention relates to a virtual metrology based method for predicting machining quality of a machine tool.
2. Description of Related Art
In the machine tool industry, machined accuracy of a workplace by a machine tool is useful for identifying whether the workplace meets design tolerances, thereby recognizing machining quality of the machine tool, so as to align, calibrate, and certify the machine tool or to stop machining operations accordingly to prevent subsequent workpieces from being out of tolerance.
Conventionally, machined accuracy of the workplace can be measured by two approaches: air off-machine measurement and an on-machine measurement. The off-machine measurement approach only samples machined workpieces for measuring their machined accuracy with dedicated measuring machines, such as a coordinate measuring machine (CMM). Compared to the on-machine measurement approach, the off-machine measurement approach may provide better accuracy of the workpiece measurement, and requires fewer time and cost for the workpiece measurement because only few sampled workpieces are measured. However, the sampling interval between two workpiece measurements is usually more than several hours. Thus, adopting off-machine workpiece measurement may suffer from the risk of producing considerable defective or out-of-tolerance workpieces if the performance of the machine tool deviates from a normal state within the sampling interval.
The on-machine measurement approach measures every machined workpiece with probes fixed on the machine tool by using a measurement method such as a probe, laser or image processing technique. Compared to the off-machine measurement approach, the on-machine measurement approach may provide relatively prompt measurement results. Nevertheless, the on-machine measurement requires sacrificing the available machining time of a machine tool for performing measurements, thus reducing the availability of the machine tool. Besides, to equip all of the factory-wide machine tools with measuring devices will bring significant cost to the on-machine measurement approach.